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Old 07-31-2012, 09:22 AM   #1
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car speed

I just got some 225/50/16 tires would the speed be wrong on the car. The car is a 87 gt
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Old 07-31-2012, 09:35 AM   #2
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Re: car speed

if the overall height is the same its fine

to find this take the stock tire that came on the rim

multiply the first number by the middle number divided by 100, thats the height (in MM) of the sidewall.

For example 255 * (50/100) => 255 * .50 => 127.50mm

If your rim size changes on the stock vs new rims simply figure that in. If the stock rims are 15in rims and the new ones are 16in rims then you gained 1 inch in rim size. Thats .5 inches top and .5 inches bottom (half/half)

every 1 inch = 25.4 mm.

If you went up from a 15in rim to a 16in rim then the tire height needs to come down half an inch so the overall diameter is correct.

soooooo.............


255/50/16 = 127.5mm

If you had 15 inch tires the height would need to be 140.2mm


or to keep it simple

255/50/16:

255(width) * (50/100) (sidewall height) * 2 (top and bottom) + (15(rim size) * 25.4(convert rim to MM))

255 * (50/100)* 2 + (15 * 25.4)

255 * .50 * 2 + (15 * 25.4)

127.50 * 2 + (15 * 25.4)

127.50 * 2 + 381

255 + 381 = 636mm

and 636mm / 25.4 = 25.04 inches (which should be the overall height of the tire ground to top)
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Old 07-31-2012, 11:20 AM   #3
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There is also a tire converter in the useful stick thread.
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Old 07-31-2012, 12:25 PM   #4
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Quote:
Originally Posted by kickerofdoom
I just got some 225/50/16 tires would the speed be wrong on the car. The car is a 87 gt
You can use an app on the iPhone I have to check its usually right on maybe 1 mpg +/- but usually correct
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Old 07-31-2012, 08:27 PM   #5
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255/50/16 is the tire size I need
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